Desulfurization of hydrocarbons by ionic liquids and preparation of ionic liquids

ABSTRACT

The present invention relates to an improved desulfurization process using an ionic liquid compound of general formula C + A − , where C +  represents an organic cation such as alkyl-pyridinium, di-alkyl imidazolium and tri-alkyl imidazolium; and A −  is an anion of halides of iron (III), such as, for example, FeCl 4   − . The desulfurization process is also improved when producing the ionic liquid compound by heating the reactants using microwave energy. The ionic liquids can be used to desulfurize hydrocarbon mixtures by a liquid-liquid extraction.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional application of Ser. No. 12/471,846,filed May 26, 2009, which claims priority to Mexican Patent ApplicationNo. MX/a/2008/006731, filed on May 26, 2008, in the Mexican PatentOffice, the disclosure of which is hereby incorporated by reference inits entirety.

FIELD OF THE INVENTION

This invention provides a process for the synthesis of ionic liquidswhich can be used for the efficient removal of sulfur compounds fromhydrocarbon mixtures. The ionic liquids related are insoluble inhydrocarbons but are able to dissolve aliphatic and aromatic sulfurcompounds. Thus, the ionic liquids can be used for removal of sulfurcompounds by a liquid-liquid extraction process at room temperature andpressure. The invention is also directed to a process for extractingsulfur from a hydrocarbon liquid by contacting the hydrocarbon with theionic liquid.

More preferably, this invention is related to the synthesis of ionicliquids with general formula C⁺A⁻, where C⁺ is an organic cationpreferably but not exclusively alkyl pyridinium, dialkylimidazolium, andtrialkylimidazolium, the anion A⁻ is preferably halogen ferrate (III),particularly Cl*FeCl₃ ⁻ and Br*FeCl₃. The invention is also directed tothe process for the extraction of sulfur-containing compounds, such assulfur compound that are present in gasoline and Diesel as contaminantobtained in petroleum refining processes by contacting with the ionicliquids.

BACKGROUND OF THE INVENTION

The production of gasoline according with the new European EnvironmentalStandards requires that the refiners to lower the sulfur content ingasoline to values that are lower than 50 ppm since 2005. For example inGermany he content of sulfur in gasoline should be lower than 10 ppm.For the case of USA the content of sulfur is limited to lowest than 80ppm and with average of 30 ppm. In attention to this claims, PEMEXRefining should be produce gasoline with sulfur content between 15 and30 ppm for the years 2008-2010.

The classic method used for sulfur removal in Refining Processes is thecatalytic Hydrodesulfurization (HDS technology) at high temperature andpressure. This method is very costly process that required drasticoperation conditions and it is inefficient to reduce aromatic sulfurcompounds especially for Mexican heavy crude oil, so is more reasonablethe use of alternative desulfurization process. For increasing theefficiency of HDS process some technology modification are required suchas the addition of other catalytic bed, more efficient catalyst, highertemperature and pressures and to reduce LHSV to expense of fewprocessing capacity.

New technologic lines have been develop on in several countries in orderto resolve this problem (Zaczepinski, S. Exxon, Diesel Oil DeepDesulfurization (DODD) in Handbook of Petroleum Refining Processes, ed.R. A. Meyer, Mc Graw-Hill, NY, 1996, Ch. 8.7), i.e.: the absorption ofsulfur compounds over solid absorbents, like IRVAD® process (U.S. Pat.No. 5,730,860, dated Mar. 24, 1998) from Black & Veatch Pritchard Inc.;the process S-Zorb® from Phillips Petroleum(http://www.eia.doe.gov/oiaf/servicerpt/ulsd/uls.html), the processHaldor Topsoe (EP 1057879, dated Dec. 6, 2000); and the liquid-liquidextraction with volatile organic solvents (Petrostar Refining, 217National Meeting, American Chemical Society, Anaheim, Calif., Marzo,1999). An original process is the oxidative desulfurization withdifferent oxidant agents (Unipure Corp., NPRA Meeting No AM-01-10, Marzo2001; Sulphco Corp, NPRA Meeting No AM-01-55, March 2001; BP ChemicalsUK, Journal of Molecular Catalysis A: Chemical (1997) 397-403; UOP LLC,U.S. Pat. No. 6,171,478, dated Jan. 9, 2001; EXXON Research andEngineering Co., U.S. Pat. No. 5,910,440, dated Jun. 8, 1999; U.S.Patent Publication No. 2002/0035306 A1 with publication date of Mar. 21,2002; U.S. Pat. No. 6,596,914 B2, dated Jul. 22, 2003; U.S. Pat. No.6,406,616, dated Jun. 18, 2002 and U.S. Pat. No. 6,402,940 B1 dated Jun.11, 2002; Fuel 82 (2003) 4015; Green Chemistry 5 (2003) 639). Recentlythe extraction of sulfur-containing compounds using liquid-liquidextraction employing ionic liquids have been welcome by scientificcommunity.

Ionic liquids are known for more than 30 years, but their industrialapplications began in the last 10 years (Rogers, R. D.; Seddon, K. R(Eds.), Ionic Liquids: Industrial Applications of Green Chemistry, ACS,Boston, 2002). They are applied as solvents and catalyst in alkylationreactions, polymerization and Diels-Alder cycloaddition. In additionthey are employed in electrochemical processes, in supercritical CO₂extraction of aromatic compounds and sulfur compounds in hydrocarbonmixtures. One of the first publications mention the use of ionic liquidsfor the removal of mercaptans (WO 0234863, dated May 2, 2002). Thepatented method is based on the use of sodium hydroxide in combinationwith ionic liquids for the conversion of mercaptans to mercaptures,which were removed using ionic liquids. Peter Wassercheid and coworkerspublished several papers and patents between 2001 and 2005 about the useof ionic liquids for desulfurization of gasolines (Chem. Comun. (2001)2494; WO 03037835, with publication date of 2003 May 8; U.S. PublicationNo. 2005/0010076 A1, published Jan. 13, 2005). In these works theauthors employed ionic liquids with C⁺ being 1,3-dialkylimidazolium ortetralkylammonium, and A⁻ being tetrachloroaluminates ormethanesulfonates. By means of a process with several extractions (up to8 extractions), high extraction of sulfur compounds were achieved usingmodel gasolines. However these kinds of compounds are air and moisturesensitive and a polymerization reaction was observed during theextraction process. U.S. Patent Publication No. 2003/0085156 A1published May 8, 2003 and U.S. Pat. No. 7,001,504, dated Feb. 21, 2006,also mention the use of ionic liquids, where C⁺ is an ammonium ofosfonium and quaternary, A⁻ being tetrachloroaluminates for theextraction of sulfur from model gasoline. In the paper published inEnergy & Fuels 18 (2004) 1862, the use of ionic liquids containingCopper chloride (I) anion with the same application, and in the papersInd Eng. Chem. Res. 43 (2004) 614 and Ind. Eng. Chem. Res. 46 (2007)5108-5112) several ionic liquids were evaluated for the extraction ofsulfur and nitrogen-containing compounds. More recently, some papers(Energy & Fuels 20 (2006) 2083-2087; Green Chemistry 8 (2006) 70-77;Progress in chemistry 19 (2007) 1331-1344; Green Chemistry 10 (2008)87-92) also report the use of IL for desulfurization processes. U.S.Patent Publication No. 2004/00445874 A1, published Mar. 11, 2004,discloses a procedure for desulfurization and denitrogenation ofhydrocarbons fractions using a wide family of ionic liquids andalkylations agents with high efficiency in some cases.

SUMMARY OF THE INVENTION

The present invention is directed to the use of ionic liquids containinghalogens of Fe (III) as an anion for these purposes, where thesecompounds presented very high efficiency for extractingsulfur-containing compounds from gasoline, turbosin, diesel and otherpetroleum fractions. Another important and novel aspect of the inventionis the use of microwave irradiation for synthesizing the ionic liquidssuitable for use as extracting agents (symmetric and non-symmetriccompounds) with a corresponding shorter time and higher yields in thesynthesis of these ionic liquids compared to the conventional methods ofsynthesis.

The invention is also directed to a process for extracting sulfur andsulfur compounds from a sulfur-containing hydrocarbon liquid bycontacting the hydrocarbon liquid with an ionic liquid of the inventionfor sufficient time to extract the sulfur and sulfur-containingcompounds, and thereafter recovering the hydrocarbon liquid.

The ionic liquids of the invention comprise a heterocyclic cation and aniron (III) halide. The heterocyclic cation is an imidazolium compoundhaving at least one C₁-C₁₀ alkyl group or alkoxy group where the alkylgroup and alkoxy group can be linear, branched, substituted orunsubstituted. The heterocyclic cation can be symmetrical orasymmetrical.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to the field of the synthesis of new ionicliquids and their application for the desulfurization of hydrocarbonfractions by means a liquid-liquid extraction (ionic liquid-hydrocarbonfraction) method. This removal of sulfur compounds is carried out due tothe higher affinity among sulfur-containing compounds and the ionicliquid media with respect to the very low polarity of the hydrocarbonmedia. By means a vigorous stirring between the low immiscible phasesfollowing by phase separation step, the sulfur content in thehydrocarbon phase is considerably reduced.

The Ionic Liquids

The ionic liquids employed in this invention present the general formulaC⁺A⁻, where C⁺ is an organic cation, and A⁻ is the anion. The cation canbe, for example, an alkylpyridinium, alkylimidazolium,dialkylimidazolium, hydroxy-alkyl alkyl imidazolium and1,2,3-trialkylimidazolium, A⁻ is FeCl₄ ⁻ or a derivative thereof.

The ionic liquids of this invention were derived from cations producedfrom imidazol and pyridine derivatives. The imidazol and pyridinecations can have the following formula:

Imidazolium:

wherein the imidazole nucleus may be substituted with at least one groupselected from a linear or branched C₁-C₁₀ alkyl, a linear or branchedC₁-C₁₀ alkoxy group and functionalized alkyl groups having oneheteroatom selected from N, O and S or halogen atoms.

R₁, R₂, and R₃ are independently selected from a group consisting ofhydrogen; linear or branched, saturated or unsaturated, aliphatic oralicyclic alkyl groups having from 1 to 10 carbon atoms; a linear orbranched alkoxy group or functionalized alkyl groups, having oneheteroatom selected from N, O and S or halogen atoms.

The alkyl and alkoxy groups have 1 to 10 carbon atoms, and preferably 2to 8 carbon atoms. In one embodiment, R₁ is a hydrogen or a methylgroup. The R₁ and R₂ groups can be the same to define a symmetricalionic liquid or different to define an asymmetrical ionic liquid. Inanother embodiment, R₁ is methyl, R₂ is a hydrogen or methyl, and R₃ isa C₂-C₈ alkyl. The R₃ alkyl group can be a methyl, ethyl, propyl orbutyl group. In one preferred embodiment, R₃ is a butyl group. The alkylgroup can be substituted with a functional group such as a hydroxygroup. In one embodiment, R₃ is a 2-hydroxyethyl group. In anotherembodiment, R₁ is methyl, R₂ is a hydrogen atom or methyl, and R₃ is aC₂-C₈ alkyl which can be substituted or unsubstituted.

Pyridinium:

wherein the pyridine nucleus may be substituted with at least one groupselected from a linear or branched C₁-C₁₀ alkyl.

R₁, and R₂ are independently selected from group consisting of hydrogen;linear or branched, saturated or unsaturated, aliphatic or alicyclicalkyl groups having from 1 to 10 carbon atoms.

In one embodiment, R₁ is a hydrogen atom or a alkyl group and R₂ is alinear or branched alkyl group. R₁ and R₂ can be a linear or branchedalkyl group having 1 to 10 carbon atoms, and preferably 2 to 8 carbonatoms. In one embodiment, R₁ is a hydrogen and R₂ is an actyl group. Inboth cases the anion is of the FeCl₄ ⁻ type.

Synthesis of the Ionic Liquids

For non-symmetrical ionic liquids, the synthesis is made in two steps,based on the alkylation method and metathesis of anion, (refs:Tetrahedron 2003, 59, 2253-2258; New J. Chem. 2002, 26, 1667-1670; J.Org. Chem. 2005, 70, 7882-7891; Green Chem. 2003, 5, 181-186; Inorg.Chem. 2001, 40, 2298-2304; J. Chem. Eng. Data 2006, 51, 691-695). In thefirst step the following reaction is carried out; and the subsequentreactions, this nomenclature is used:

Nomenclature:

-   Im=Imidazole-   (CH₃)₃SiNHSi(CH₃)₃=Hexamethyldisilazane-   Im-Si(Me)₃=N-(Trimethylsilyl)imidazol-   (CH₃)₃SiNH₂=Trimethylsilylamine-   Cl-Alq=Alkyl chloride-   Alq-Im⁺-Alq Cl⁻=Dialkyl imidazolium chloride-   Alq-Im⁺-Alq FeCl₄ ⁻=Dialkyl imidazolium tetrachloroferrate-   HetCic-N=Heterocycle with nitrogen-   HetCic-N⁺-Alq Cl⁻=Alkyl imidazolium chloride-   HetCic-N⁺-Alq FeCl₄ ⁻=Alkyl imidazolium tetrachloroferrate

HetCic-N+Cl-Alq-^(Δ)→HetCic-N⁺-Alq Cl⁻  I)

In the second step the alkyl imidazolium chloride reacted with ironchloride (III), obtaining the ionic liquid with anion FeCl₄ ⁻:

HetCic-N⁺-Alq Cl⁻+Fe Cl₃→HetCic-N⁺-Alq FeCl₄ ⁻  II)

The first step of synthesis takes place heating by microwavesirradiation, with which the times of reaction diminish from the 95 to98%, to comparison with conventional heating synthesis.

In the case of symmetrical ionic liquids, the synthesis is carried outin three steps, based in the method of activation of secondary nitrogenwith the trimethylsilyl group, alkylation and metathesis of anion,(refs.: Polymer 2004, 45, 5031-5045; Chem. Commun. 2001, 1466-1467). Infirst, the 1-trimethylsilyl derived was synthesized from the nitrogencompound by the following chemical reaction:

Im+(CH₃)₃SiNHSi(CH₃)₃-^(Δ)→Im-Si(Me)₃+(CH₃)₃SiNH₂   I)

In the second step, both nitrogen atoms were alkylated with a alkylchloride:

Im-Si(Me)₃+2 Cl-Alq→Alq-Im⁺-Alq Cl⁻  II)

And in the third step, the precursor is reacted with FeCl₃:

Alq-Im⁺-Alq Cl⁻+FeCl₃→Alq-Im⁺-Alq FeCl₄ ⁻  III)

Of the same way that for not-symmetrical the ionic liquids, thesymmetrical ones are synthesized with the use of the microwaves likenonconventional source of heating, with which the times of reaction isdiminish more than 90%, with comparable yields respect to conventionalmethod.

To continuation some examples are described, and are not intended tolimit the scope of the present invention.

EXAMPLE 1 Synthesis of 1-butyl-3-methylimidazolium tetrachloroferrate([BMIM]FeCl₄)

Step 1: In glass reactor, 1.64 g (20 mmol) of 1-methylimidazole wasmixed with 5.55 g (60 mmol) of 1-chlorobutane. After 48 hours ofstirring and refluxing with conventional heating, the two-phase mixturewas formed. The top layer was decanted off. The residue was washed withethyl acetate (3×20 ml) and vacuum dried at 90° C. for 5 hours. Aviscous colorless liquid was obtained (yield 70%)

Step 2: In glass reactor that is equipped with a magnetic stirringmechanism 0.87 g (5 mmol) of 1-butyl-3-methylimidazolium chloride,obtained from step 1, was introduced and 1.22 g (7.5 mmol) of ironchloride (III) anhydrous was added. The mixture was stirred for 20minutes at room temperature under an inert atmosphere. A dark red liquidwas obtained. The spectroscopic characterizations (¹H and ¹³C NMR)confirm the following chemical structure:

EXAMPLE 2 Synthesis of 1-butyl-2,3-dimethylimidazoliumtetrachloroferrate ([BDMIM]FeCl₄)

Step 1: The 1-butyl-2,3-dimethylimidazolium chloride was obtained (yield86%) in the same manner described in Example 1 (Step 1) with theexception that 1,2-dimethylimidazole was used instead of1-methylimidazole.

Step 2: In glass reactor that is equipped with a magnetic stirringmechanism 0.94 g (5 mmol) of 1-butyl-2,3-dimethylimidazolium chloridewas introduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrouswas added. The mixture was stirred for 20 minutes at room temperatureunder an inert atmosphere. A dark red liquid was obtained.

EXAMPLE 3 Synthesis of 1,3-dibutylimidazolium tetrachloroferrate([DBIM]FeCl₄)

This ionic liquid can be obtained by two alternative procedures andusing the conventional heating or the microwaves irradiation as theheating source.

Procedure 1

Step 1: The 1,3-dibutylimidazolium chloride was obtained (yield 90%) inthe same manner described in Example 1 (Step 1) with the exception that2.48 g (20 mmol) of 1butylimidazole was used instead of1-methylimidazole.

Step 2: In a glass reactor equipped with a magnetic stirring mechanism1.08 g (5 mmol) of 1,3-dibutylimidazolium chloride was introduced and1.22 g (7.5 mmol) of iron chloride (III) anhydrous was added. Themixture was stirred for 20 minutes at room temperature under an inertatmosphere. A dark red liquid was obtained.

Procedure 2

This procedure consists of three steps.

Step 1 (Synthesis of 1 (trimethylsilyl)-imidazol): In a reactor 1.36 g(20 mmol) of imidazol and 4.85 g (30 mmol) of1,1,1,3,3,3-hexamethyldisilazanol was mixed under an inert atmosphere.The mixture was refluxing for 12 hrs. The reaction formedN-trimethylsilyl-imidazol which was distilled under reduced pressure toafford a viscous colorless liquid (yield 95%).

Step 2 (Synthesis of 1,3-dibutylimidazolium chloride): In a reactor, toa mixture formed by 1.40 g (10 mmol) of N-trimethylsilyl-imidazolobtained previously and 2.78 g (30 mmol) of 1-chlorobutane was added 30ml of toluene. After 48 hours of stirring and refluxing, the two-phasemixture was formed. The top layer was decanted off. The residue waswashed with ethyl acetate (3×20 ml). Removal of the solvent underreduced pressure afforded a viscous colorless liquid (yield 60%)

Step 3: In a glass reactor that is equipped with a magnetic stirringmechanism 1.08 g (5 mmol) of 1,3-dibutylimidazolium chloride wasintroduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrous wasadded. The mixture was stirred for 20 minutes at room temperature underan inert atmosphere. A dark red liquid was obtained.

The described compound also was synthesized according to the twoalternative procedures previously described, but using microwaveirradiation (300 W) for 15 minutes of irradiation for step 1 of thefirst alternative procedure and for 10 minutes and 20 minutes ofirradiation for steps 1 and 2 of alternative procedure 2, to obtain thecompound in quantitative yields.

EXAMPLE 4 Synthesis of N-octylpyridinium tetrachloroferrate ([OP]FeCl₄)

Step 1: N-octylpyridinium chloride was obtained (yield 68%) in the samemanner described in Example 1 (Step 1) with the exception that 1.58 g(20 mmol) of pyridine was used instead of 1-methylimidazole and 8.92 g(60 mmol) of 1-chlorooctane was used instead of 1-chlorobutane

Step 2: In a glass reactor equipped with a magnetic stirring mechanism1.14 g (5 mmol) N-octylpyridinium chloride, obtained from step 1, wasintroduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrous wasadded. The mixture was stirred for 20 minutes at room temperature underan inert atmosphere. A dark red liquid was obtained. The spectroscopiccharacterizations (¹H and ¹³C NMR) confirm the following chemicalstructure:

EXAMPLE 5 Synthesis of 1-(2-hydroxyethyl)-3-methylimidazoliumtetrachloroferrate ([HEMIM]FeCl₄)

Step 1: The 1-(2-hydroxyethyl)-3-methylimidazolium chloride was obtainedwith a 90% yield. In a reactor, to a mixture formed by 11.64 g (20 mmol)of 1-methylimidazole and 3.2 g (40 mmol) 2-chloroethanol was added 30 mlof toluene. After 48 hours of stirring and refluxing, the two-phasemixture was formed. The top layer was decanted off. The residue waswashed with ethyl acetate (3×20 ml). Removal of the solvent underreduced pressure afforded a viscous colorless liquid.

Step 2: In a glass reactor equipped with a magnetic stirring mechanism0.81 g (5 mmol) of 1-(2-hydroxyethyl)-3-methylimidazolium chloride wasintroduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrous wasadded. The mixture was stirred for 20 minutes at room temperature underan inert atmosphere. A dark red liquid was obtained. The spectroscopiccharacterizations dates (¹H and ¹³C NMR) confirm the following chemicalstructure:

Tests of Performance of Ionic Liquids for Desulfurization ofHydrocarbons

The ionic liquids of the invention can be used in a process forextracting sulfur and sulfur compounds from a hydrocarbon liquid bycontacting the hydrocarbon liquid with the ionic liquid.

The evaluations were performed with a mixture model prepared through thedissolution of benzothiophene and thiophene in equal parts, in ahexane/heptane mixture (1:1), having a total sulfur concentration of 500ppm. The extraction tests were done by contacting 1 part of ionic liquidwith 5 parts of the mixture model (weight/weight, w/w), in such a waythat the extraction process was made with a relation weight of ionicliquid to hydrocarbon. The ionic liquid can be contacted with thehydrocarbon liquid at a ratio of about 1:1 to 1:20 (w/w), and preferablya ratio of about 1:1 to 1:10 (w/w). The determination of the sulfurcontent was determined by x-ray diffraction.

To 5.0 g of a model mixture (that contained 500 ppm of sulfur) 1.0 g ofcorresponding ionic liquid was added (obtained from examples 1-5); inthe reaction mixture two phases were formed, after 30 min of agitationat room temperature. The ionic liquid phase was separated form the modelmixture.

In Table 1 are the obtained results.

TABLE 1 Hydrocarbon sulfur removal by extraction with ionic liquids.Final sulfur content in % of total removed Ionic liquid hydrocarbon(ppm) sulfur in hydrocarbon 1* >10 99 2* >10 99 3* 14 97 4* 152 70 5*325 35 *Notes: 1*: 1-butyl-3-methylimidazolium tetrachloroferrate. 2*:1-butyl-2,3-dimethylimidazolium tetrachloroferrate. 3*:1,3-dibutylimidazolium tetrachloroferrate. 4*: N-octylpyridiniumtetrachloroferrate. 5*: 1-(2-hydroxyethyl)-3-methylimidazoliumtetrachloroferrate.

As observed in Table 1, the ionic liquids with the tetrachloroferrateanion can almost quantitatively remove the sulfur content of the sampleoriginal model, especially the ionic liquids with imidazolium cation.Thus, the ionic liquids can be used for the deep desulfurization ofhydrocarbon mixtures, such as, gasoline, diesel engine fuel, kerosene,jet fuel and light cyclical oil.

While various embodiments have been chosen to illustrate the invention,it will be understood that various changes and modifications can be madewithout departing from the scope of the invention as recited in theappended claims.

What is claimed is:
 1. An ionic liquid for the desulfurization ofhydrocarbons, comprising a heterocyclic cation and an iron (III) halideanion wherein said ionic liquid is capable of removing sulfur and sulfurcompounds from a liquid hydrocarbon.
 2. The ionic liquid according toclaim 1, wherein the ionic liquid is symmetrical or asymmetrical and theheterocyclic cation is imidazolium or a derivative thereof having linearor branched, saturated or unsaturated, aliphatic or alicyclic alkylgroups having from 1 to 10 carbon atoms; linear or branched alkoxygroups or functionalized alkyl groups having one heteroatom selectedfrom the group consisting of N, O and S or halogen atoms.
 3. The ionicliquid according to claim 2, wherein the anion is a halide of iron (III)derived from FeCl₃.
 4. The ionic liquid according to claim 2, whereinsaid heterocyclic anion has the formula

R₁, R₂, and R₃ are independently selected from group consisting ofhydrogen; linear or branched, saturated or unsaturated, aliphatic oralicyclic alkyl groups having from 1 to 10 carbon atoms; linear orbranched alkoxy groups or functionalized alkyl groups having oneheteroatom selected from N, O and S or halogen atoms and the anion isFeCl₄ ⁻.
 5. The ionic liquid according to claim 4, wherein theimidazolium cation is symmetrical when R₁ is the same as R₂ orasymmetrical where R₁ is not the same as R₂.
 6. The ionic liquidaccording to claim 1, wherein said heterocyclic anion has the formula

wherein the pyridine nucleus is substituted with at least one groupselected from a linear or branched C₁-C₁₀ alkyl.
 7. The ionic liquidaccording to claim 6, wherein R₁, and R₂ are independently selected fromgroup consisting of hydrogen, linear or branched, saturated orunsaturated, aliphatic or alicyclic alkyl groups having from 1 to 10carbon atoms.
 8. The ionic liquid according to claim 6, wherein R₁ is ahydrogen atom and R₂ is a C₂ to C₁₀ alkyl group and the anion is FeCl₄⁻.
 9. A process for the synthesis of a symmetrical ionic liquid of claim2, comprising the steps of: activating a secondary nitrogen with atrimethylsilyl group according to the following reaction step to form a1-trimethylsilazane and N-trimethylsilylimidazol:Im+(CH₃)₃SiNHSi(CH₃)₃-^(Δ)→Im-If(Me)₃+(CH₃)₃SiNH₂   I) alkylizing thereaction product with an alkyl chloride according to the followingreaction step:Im-If(Me)₃+2 CL-Alq→Alq-Im⁺-Alq CL⁻  II) and treating the precursor withFeCl₃ to produce an dialkylimidazolium tetrachloroferrate according tothe following reaction step:Alq-Im⁺-Alq CL⁻+FeCl₃→Alq-Im⁺-Alq FeCl₄ ⁻  III) where: Im=Imidazolium(CH₃)₃SiNHSi (CH₃)₃=Hexamethylbisilazane Im-If(Me)₃=N-Trimethylsilylimidazolium (CH₃)₃SiNH₂=TrimethylsilylamineCL-Alq=Alkyl chloride Alq-Im⁺-Alq CL⁻=Dialkyl imidazolium chlorideAlq-Im⁺-Alq FeCl₄ ⁻=Dialkylimidazolium tetrachloroferrate
 10. A processfor the synthesis of asymmetrical ionic liquids of claim 2, comprisingthe steps of:HetCic-N+CL-Alq-^(Δ)→HetCic-N⁺-Alq CL⁻  I) and treating the reactionproduct of step I with FeCl₃ to form an alkylimidazoliumtetrachloroferrate according to the following reaction:HetCic-N⁺-Alq CL⁻+Faith CL₃→HetCic-N⁺-Alq FeCl₄ ⁻  II) where:HetCic-N=Heterocycle with nitrogen HetCic-N⁺-Alq CL⁻=Alkyl imidazoliumchloride HetCic-N⁺-Alq FeCl₄ ⁻=Alkyl imidazolium tetrachloroferrate 11.The process of claim 9, wherein the first and second steps comprisesirradiating the reaction mixture with microwave energy for 10 min. to 1hr.
 12. The process of claim 10, wherein said first step comprisesirradiating the reaction mixture with microwave energy for 10 min. to 1hour.
 13. An ionic liquid composition comprising a hydrocarbon liquidcontaining sulfur compounds, and an ionic liquid in an amount sufficientto remove the sulfur compounds from hydrocarbon liquid, said ionicliquid has a heterocyclic cation and an iron (III) halide anion.
 14. Theionic liquid composition according to claim 13, wherein the ionic liquidis symmetrical or asymmetrical and the heterocyclic cation isimidazolium or a derivative thereof having linear or branched, saturatedor unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 10carbon atoms; linear or branched alkoxy groups or functionalized alkylgroups having one heteroatom selected from the group consisting of N, Oand S or halogen atoms.
 15. The ionic liquid composition according toclaim 14, wherein the anion is a halide of iron (III) derived fromFeCl₃.
 16. The ionic liquid composition according to claim 14, whereinsaid heterocyclic anion has the formula

R₁, R₂, and R₃ are independently selected from group consisting ofhydrogen; linear or branched, saturated or unsaturated, aliphatic oralicyclic alkyl groups having from 1 to 10 carbon atoms; linear orbranched alkoxy groups or functionalized alkyl groups having oneheteroatom selected from N, O and S or halogen atoms and the anion isFeCl₄ ⁻.
 17. The ionic liquid composition according to claim 16, whereinthe imidazolium cation is symmetrical when R₁ is the same as R₂ orasymmetrical where R₁ is not the same as R₂.
 18. The ionic liquidcomposition according to claim 13, wherein said heterocyclic anion hasthe formula

wherein the pyridine nucleus is substituted with at least one groupselected from a linear or branched C₁-C₁₀ alkyl.
 19. The ionic liquidcomposition according to claim 18, wherein R₁, and R₂ are independentlyselected from group consisting of hydrogen, linear or branched,saturated or unsaturated, aliphatic or alicyclic alkyl groups havingfrom 1 to 10 carbon atoms.
 20. The ionic liquid composition according toclaim 18, wherein R₁ is a hydrogen atom and R₂ is a C₂ to C₁₀ alkylgroup and the anion is FeCl₄ ⁻.